What is a credible offsetting and removal of emissions strategy?
At a planetary scale, we are already committed to requiring large-scale offsetting of emissions to achieve net zero. Even if we accelerate decarbonization at rates never achieved before, reducing emissions is not going to be enough. The active removal of greenhouse gases from the atmosphere at a massive scale is going to be necessary - and is already assumed within models designed to inform policy. According to these models, to restrict warming to less than 1.5 degrees, it will be necessary to remove hundreds of billions of tonnes from the atmosphere in the decades ahead.
While it is possible to decarbonise some sectors of the economy (such as power generation and land transport), other sectors (such as aviation and cement production) are much harder to decarbonise. In order to achieve net zero, it is therefore necessary to match each tonne of CO2 emitted from a hard-to-decarbonise sector with an equivalent amount of carbon dioxide removed from the atmosphere and permanently stored away.
What offsets are and how to use them.
The notion of offsetting is intrinsic to the concept of Net Zero. Since the combustion of fossil fuel is effectively irreversible over less than geological timescales, the only sinks that can be relied upon to offset any remaining fossil CO2 emissions must also be effectively irreversible. Great care must be taken that such removal processes are robust - that the overall carbon footprint of such processes actually results in removal, and that the removal is permanent, rather than temporary.
There is a danger of false offsets - ones that either overstate the amount of removal, or worse do not result in net removal at all. While there are many people selling offsets, there is a distinct lack of standards and regulation, with the result that there are many poor-quality offsets available. There is a clear need for regulation in this space to prevent abuses and to ensure good-quality offsets are not tarnished by phoney offsets.
Hard vs. soft offsets
‘Hard offsets’ are offsets in which greenhouse gas sources are netted against greenhouse gas sinks that have a very high degree of “permanence” (the expected duration of storage), for example, carbon stored deep underground in geologically stable formations.
Most commercially available offsets are ‘soft offsets’ - offsets in which emissions are netted against an avoided emission or a natural carbon sink with a shorter or more uncertain degree of permanence. Forestry projects for air travel are examples of soft offsets. During the decades-long period during which trees grow they remove CO₂ from the air, but the CO₂ only remains removed if the mature forest is permanently maintained. If, at a future point in time, the trees are chopped down or burnt the CO₂ is re-released back into the air. So, while offset-providers typically provide 100% of the CO₂-removal credits to the purchaser of the offsets as soon as the trees are planted, there is no guarantee that the offset will be permanent.
A credible offsetting of emissions strategy
A credible offsetting strategy which can claim to be achieving net zero must be such that by the desired ambition date, 100% of offsets for unavoided emissions must store carbon with very high permanence on a geologic time scale. Furthermore, it should be able to demonstrate that they are on a pathway, with near term progress, from soft to hard offsets. And until 100% of offsets are hard offsets, soft offsets must be single- counted, additional, measurable and verifiable permanent emission reductions.
Offsets against avoided emissions, such as funding for energy efficiency or renewable projects in the developing world, can only be said to have resulted in an emissions reduction if the offsetting project can prove ‘additionality’. That is that the reduction would not have ever occurred without the carbon offsetting project. This type of projects can be valuable now at fostering rapid decarbonization, but is not enough to achieve ‘net zero’.
What are Greenhouse Gas Removal techniques?
Greenhouse Gas Removal (GGR) techniques actively remove greenhouse gases from the atmosphere and reliably store them for at least 1,000 years- preferably for 10,000 years. The three broad categories of GGR involve natural processes (Nature-based Solutions), engineered approaches, and permanent storage of carbon dioxide.
Currently, GGR techniques cost more than conventional methods of emissions reduction like enhanced energy efficiency, renewable energy generation, and electrification. However, the IPCC has shown that GGR technologies will be needed to limit warming to less than 2°C cost-effectively. They are needed for hard-to-decarbonise sectors such as transport, agriculture, steel, aviation, cement, and chemical production.
There are many types of GGR technologies but here are a few of the most promising:
Bioenergy with CCS (BECCS) - Grow crops to suck carbon out of the air, burn them to generate electricity, capture the CO2 emissions from combustion, compress and store that captured CO2 in geologically inert underground reservoirs (e.g. spent oil wells, underground saline formations), and monitor the stored CO2 to ensure it doesn’t leak back out.
BECCS is a more specific version of Carbon Capture and Storage (CCS), the general term for capturing and sequestering CO2. Most conventional CCS projects involve separating a waste stream of CO2 from a large point source (e.g. power plant, cement factory), which is a helpful way of reducing emissions, but is not a removal technology. The oil and gas industry has used carbon capture and transportation for decades. In total, there are as many as 18 large-scale carbon capture storage (CCS) projects in operation, five under construction, and 20 further planned projects. One significant barrier to accelerated development and deployment is a lack of incentive due to high costs and market uncertainty.
Direct Air Capture (DAC) - Filter and / or chemically concentrate CO2 out of thin air, compress it, and store it in geologically inert underground reservoirs. These processes currently require vast amounts of energy and are prohibitively expensive for now.
Regulation is needed to determine the cost of carbon emissions or/and implement a robust carbon certification and trading scheme.
What are Nature-based Solutions?
Nature-based Solutions involve working with and enhancing nature to reduce greenhouse gas emissions while addressing societal goals. They can contribute to achieving net zero emissions by capturing carbon dioxide through natural processes such as photosynthesis.
Nature-based Solutions include reforestation, wetland restoration, green roofs, integrated water resource management, and protected parks.
What role do nature-based solutions play in achieving net zero emissions?
Nature is vulnerable to climate change impacts, such as increased forest fires, that are beyond our control. Therefore, nature-based solutions can not be used as an alternative to keeping fossil fuels in the ground. They should merely complement the primary goal of decarbonising the economy.
How do GGR techniques impact broader society?
GGR techniques use resources. For example, DACCS and enhanced weathering require energy, while high levels of BECCS can put a strain on the land area and freshwater reserves needed to grow the necessary feedstocks. Therefore, GGR technologies must be developed with consideration to sustainability and equity on international, and intergenerational scales.
Nature-based solutions pathways which do not support sustainable development need to be recognised and changed. For instance, current climate change policy for net zero emissions favour single-species tree plantations. This approach results in low diversity plantations which have low resilience to climate extremes and new diseases- thus eliminating initial benefits.
The greatest opportunities for nature-based solutions lie in protecting and restoring biodiverse ecosystems. Such solutions are predicted to have mostly positive impacts on the Sustainable Development Goals. Potential adverse effects include the use of agricultural land for afforestation. Land-use battles create food security and economic growth concerns.